The invention relates to an apparatus for coating substrates in a vacuum chamber having a cathode system or an evaporating system, which is preceded and followed by evacuable isolated chambers, the individual chambers being separable from one another by locks. In this apparatus a conduit leads into the coating chamber to supply one or more process gases, and carrier frames carrying the substrates to be coated are held and guided on rails and/or wheels and can be moved through the individual chambers.
An apparatus of the kind in question is known (EP No. 00 28 690) in which a plurality of isolated chambers are disposed in front of and behind a central coating chamber, and all of the chambers communicate through locks. The carrier frames for mounting the tabular workpieces consist of perpendicularly disposed plates each of which is equipped with a base having rollers or skids which run on a track or conveyor belt which is laid on the floor of the chambers. The locks, which separate the individual chambers from one another, are configured as rectangular flaps, and are of such dimensions that the perpendicular, tabular holders or frames with the workpieces, e.g., glass sheets, lying against them can be moved straight through the openings in the walls separating the chambers, which are uncovered by the flaps. The transport of the workpieces takes place step-wise, i.e., when all of the frames or holders mounted on the rail are simultaneously moved on chamber forward, all flaps hermetically seal off the chambers and the frames with the workpieces remain in the chambers in question for the duration of a coating operation. The entry and exit lock chambers are, like the coating chamber, connected to vacuum pumps so that the pressure in the chambers can be kept at the same level. This apparatus has the disadvantage that, when a coating operation is performed in a reactive gas atmosphere, upon each passage through a lock, i.e., upon each opening and closing of the locks between the coating chamber and the adjoining isolating chamber, the gas concentrations are altered, which then leads to irregular coating qualities, since, on the one hand, the amount of the reactive gas that is contained in the mixture of reactive gas and inert gas necessary for the process and is consumed by the reaction is of decisive importance, while on the other hand it is precisely this parameter that cannot be controlled either by pressure measurements or by flow measurements.
It is therefore the object of the present invention to create an apparatus of the kind in question, in which the process can be kept always in the same reactive state, even in dynamic operation, i.e., with substrates moving past the cathode or evaporating system, so that the coating thickness and quality will have a high degree of uniformity from substrate to substrate.
According to the invention this is achieved by one or more bypass conduits joining the coating chamber to the chamber preceding or following it, a valve or shut-off being inserted in each bypass line by which pressure equalization between the chambers can be brought about.
Preferably for this purpose valves are inserted into the suction lines connecting the chambers to the vacuum pump stands and are operated in synchronism with the valves in the bypass lines such that a closing of one valve of the exhaust line or of the particular isolation chamber produces the simultaneous or time-delayed opening of the valve in the corresponding bypass line.
By a pressure equalization performed in this manner between process and isolating chambers the assurance is automatically provided that, even during the passage of the substrate holders through the locks, the individual gas concentrations at the cathode remain constant, which is of decisive importance to the stability of the process and to the constancy of the properties of the coating.
To permit a fully automated operation, the valve regulating the flow of reactive gas into the coating chamber is coupled by a control line to the apparatus that supplies electrical energy to the cathode system, while the parameters characterizing the process, such as cathode voltage or, alternatively, cathode current, are kept constant by controlling the amount of reactive gas flowing into the coating chamber.